Project 3 will focus on as yet incompletely understood interactions between stimulus variables and motivational variables in the development of stimulus control. Making use of classic paradigms in discrimination learning, our research will investigate variables and variable interactions that may help to account for the slow and/or inconsistent learning outcomes that are frequently observed in persons with intellectual disabilities. Whereas such deficits have historically been attributed to inattention, overly broad and/or narrow attending, and/or lack of motivation, our hypothesis is that protracted discrimination learning failures can occur in individuals who would be classified as both attentive and well-motivated by traditional standards. We propose that protracted failures result when teachers/experimenters program contingencies that are indiscriminable from the perspective of the learner. The proposed project is inspired by numerous findings from our laboratories and by current quantitative theoretical analyses of learning processes that have their roots in signal detection theory (SDT). Such quantitative approaches are virtually unstudied in disability research, but we believe that they have at least two significant advantages. First, they offer a highly structured, empirically verified method for analyzing the degree to which cdtical elements of programmed contingencies are discriminable. Second, there are effective quantitative techniques for assessing the degree to which learning failures are the result of biases due to stimulus and/or reinforcer variables. Together, we believe that these two features of SDT-based analyses will help to shed light on certain longstanding problems in the analysis of learning processes of individuals with intellectual disabilities. We suggest also that a quantitative SDT-based methodology has natural advantages for supporting more effective teaching interactions for such individuals. To demonstrate these advantages, we will employ another quantitative method, the percentile-scheduling approach. By combining SDT-based analyses with percentile approaches, our goal is to establish a foundation for effective computer-based management of discrimination learning procedures of the type that are now used in educational intervention for persons with disabilities.